1. Field of the Invention
The present invention concerns a device for thickening of waste water sludges, a sewage treatment or waste-water purification plant (hereafter waste-water treatment plant), a process for minimizing the amount of decomposed sludge or, as the case may be, the residual sludge in purification plants, as well as a device for treatment of waste water.
The inventive device as well as the inventive process serve to minimize or reduce the amount of sludge produced in purification plants, to improve dewatering, and to accelerate the bio-gas fermentation during an anaerobic methane fermentation of the sludge, the waste biomass, as well as during the anaerobic purification of waste water.
In the process of biological purification of waste a relatively large amount of sludge is produced, wherein the handling thereof and the economical use often leads to problems. In the aerobic biologic purification of the waste water at least two types of sludges are produced; primary sludge--that sludge which is produced by the primary sedimentation or settling of the introduced waste water and which experiences a rapid decomposition--and as the second sludge type the activated surplus sludge, which results after the step of the biological purification of the waste water. Herein primarily a mixture of microorganisms takes part, which are produced during the waste water purification and of which the count depends upon the of the number of the impurities removed as well as on the parameters of the process during purification. Both sludge types are processed in most waste-water treatment plants, above all the larger ones, by an anaerobic methane fermentation.
The anaerobic methane fermentation of organic substances is a process, in which a mixed culture of microorganisms stepwise decomposes a biologically decomposable organic mass under anaerobic conditions. The end products of this decomposition are methane, carbon dioxide, sulfur dioxide (Sulfan), nitrogen, hydrogen, the resulting biomass and a stabilized organic material (a residual which is not further decomposable).
Among the most important factors which influence the process of the anaerobic decomposition, there are included the composition of the substrate (which determines the specific production as well as the composition of the bio-gas), the presence of nutrients, the pH-value, the buffer capacity as well as the temperature. The economical feasibility of this process is dependent upon the dry substance concentration (solid substance concentration) of the material to be processed. For this reason the starting materials are frequently subjected to a thickening process, wherein this occurs either mechanically (centrifuge, press, among others) or with the aid of gravity.
For an optimal progress of the anaerobic decomposition the presence of a series of an organic nutrients is of consequence. The presence of a series of growth factors (reproductive factors) is important as well as vitamins and enzymes. For anaerobic decomposition, above all hydrolytic enzymes are of importance, which are capable of decomposing or reducing a large number of substances such as, for example, even solid and high molecular organic substances. Several of these materials can be synthesized by the microorganisms themselves, others must be added from outside the system.
2. Description of the Related Art
A laboratory or bench top possibility for simulating the bio-gas production during anaerobic methane fermentation of sludges, waste water, as well as other various organic materials is described in CZ-PS 242 979. The process disclosed in this patent is comprised therein, that the material to be fermented has added to it, or in given cases the anaerobic reactor has added directly to it, a stimulating material which is prepared separate from the laboratory waste water purification system and which is a mechanically or physically treated microorganism-containing biomass suspension of between 0.1 up to 10 weight-%, preferably 5 weight-%, depending upon the organic dry substance of the material to be processed.
In the lytic treatment (mechanical and physical disruption of cells) of the biomass suspension according to the state of the art the content of the cells of these microorganisms is partially set free.
The content of the microorganism cells or cells of other organisms which in the course of the destruction of cell walls and/or cell membranes are released into the solution (also called cell lysate), has a facilitating or stimulating effect upon the process of biological decomposition of the organic substances. The lysate of the cells occurs on the one hand in a natural way (autolysis) with deceased cells, on the other hand with the help of hydrolytic enzymes, which are released into the solution by fermentation bacteria, and further by the artificial decomposition or dissociation of microorganisms or organisms with the help of physico-chemical or mechanical methods.
The cell lysate stimulates on the one hand the function and the growth of microorganisms, on the other hand it contains a series of enzymes, which are directly necessary for the decomposition of organic substances. The lysate stimulates the functionality or operability of certain bacteria, which convert and/or release hydrogen and carbon dioxide, acetic acids, propionic acids, etc. Besides this it strengthens the decomposition of organic materials and increases the bio-gas production in anaerobic methane producing processes which has as a consequence a reduction of the total amount of the produced sludge as well as an increase in the bio-gas production. The cell lysate can likewise significantly influence the production of surplus activated sludge when using activation tanks.
The preparation of cell lysate in laboratory scale amounts according to the state of the art is expenfiltere in terms of the equipment necessary therefor as well as the required amount of energy. This is true for the hitherto known methods of cell decomposition or destruction such as, for example, in the disruption by means of mechanical methods (grinding, milling, pressing), sonification (ultra sound treatment), cavitation, repeated freezing and thawing, heating, among others.
The above described process according to the state of the art as described in CZ-PS 242 979 has above all the disadvantage, that it requires a separate preparation of the cell lysate -external of the actual purification or treatment device. As already mentioned above, this process is only suitable on a laboratory scale; a transition to an industrial scale process is not practicable for reasons of the large space requirement, the high energy cost and investiture cost and the additional personnel requirement. So it is, for example, neither economical nor technically useful to cyclically freeze and then thaw sludge in amounts which are measured in tons.
With the state of the art as described in CZ-PS 242 979 as a starting point, it is the task of the present invention to significantly reduce the sludge amount yielded under industrial scale conditions in a less expenfiltere and in a more economical manner.